Metal thiolates of the general formula M(SR)2 (M = Pb, Zn, Cd) and Cl-Hg-SR (R = alkyl) have been prepared and characterized by spectroscopic techniques, TGA and, in selected cases, single crystal X-ray diffraction. The metal bis(thiolate) compounds can be converted into the related metal sulfides by thermolyses. The solid state materials have been characterized by XRPD, SEM and, in selected cases, by particle size determination. The volatile pyrolytic co-products have been isolated and characterized by GC/MS. The decomposition pathways of mercury chlorothiolates are more complicated and depend on the nature of the organic group present in Cl-Hg-SR.

The synthesis of oxides by the use of metal alkoxides is well known in the sol-gel process. However, little is known regarding the use of alkoxides as starting materials for nonoxides. In this work titanium isopropoxide has been reacted with different sulfidizing agents to form alkoxy sulfide precursors. In all the processes the transformation of the precursors to form TiS2 has been studied and the morphologies of the sulfide powders have also been compared. Gas chromatography and infrared spectroscopy have been used to study the molecular processes that occur in one of the reactions.

Three copper systems with relevance to materials technology are discussed. In the first, a CuS precursor, Cu4S 10(4-methylpyridine)4 (4-MePy), was prepared by three routes: reaction of Cu2S, reaction of CuBr•SMe2 and oxidation of copper powder with excess sulfur in 4-methylpyridine by sulfur. In the second, copper powder was found to react with excess thiourea (H2NC(S)NH2) in 4-methylpyridine to produce thiocyanate (NCS-) complexes. Three isolated and characterized compounds are: Cu(NCS)(4-MePy)2, a polymer, [4-MePy•H][Cu(NCS)3(4-MePy)2], a salt, and t-Cu(NCS)2(4-MePy)4. Finally, an attempt to produce a mixed-metal sulfide precursor of Cu and Ga in N-methylimidazole (N-MeIm) resulted in the synthesis of a Cu-containing polymer, Cu(S04)(N-Melm). The structures are presented; the chemistry will be briefly discussed in the context of preparation and processing of copper-containing materials for aerospace applications.

Neutral metal dithiocarbamate complexes (M(NR2CS2)x) are well-known precursors to metal sulfides, a class of materials with numerous technological applications. We are involved in a research effort to prepare new precursors to metal sulfides using simple, reproducible synthetic procedures. We describe the results of our synthetic and characterization studies for M = Fe, Co, Ni, Cu, and In. For example, treatment of metallic indium with tetramethylthiuramdisulfide (tmtd) in 4-methylpyridine (4-Mepy) at 25°C produces a new homoleptic indium (III) dithiocarbamate, In(N(CH3)2CS2)3 (I), in yields of over 60%. The indium (III) dithiocarbamate was characterized by X-ray crystallography; (I) exists in the solid state as discrete distorted-octahedral molecules. Compound (I) crystallizes in the Plbar (No. 2) space group with lattice parameters: a = 9.282(1) A, b = 10.08 1(1) Å, c = 12.502 Å, ∝ = 73.9 1(1)°, β = 70.21(1)°, γ = 85.84(1)°, and Z = 2. X-ray diffraction and mass spectral data were used to characterize the products of the analogous reactions with Fe, Co, Ni, and Cu. We discuss both use of dithiocarbamates as precursors and our approach to their preparation.

Zinc- and cadmium bis(alkylthiolate) compounds have been prepared and converted into the appropriate binary metal sulfides by thermal treatment. Several mercury chlorothiolates have been synthesized and characterized by single crystal X-ray diffraction. Their decomposition pathways are discussed. The prepared binary metal sulfides have been studied by XRPD and - in selected cases - by particle size determination. The volatile co-products have been isolated and characterized by GC/MS.

Three isomeric lead bis(butylthiolate) and tin bis(butylthiolate) compounds have been prepared and characterized. Their solid state decomposition, and in the case of the lead bis(thiolate) compounds, their thermolyses in suspension in a high boiling hydrocarbon, have been studied. X-ray powder diffraction patterns and scanning electron micrographs of the obtained solid state material are discussed. Volatile co-products of the decomposition have been isolated and characterized.

Nanocrystalline powders of 2H-MoS2 and 2H-WS2 with average particle size 5 and 9 nm, respectively, have been produced using C02laser pyrolysis. Typical production rate for these nanoparticles is 2g/hr. Particle size, crystallite size, and the structural phase were determined using X-ray diffraction(XRD), transmission electron microscopy(TEM), and Raman scattering. Particle size effects may have been observed in the Raman-active modes (WS2 and MoS2) and in the band-edge excitons (MoS2).

Solid-state 31p MAS-NMR provides powerful insights into the local order of phosphorus selenide based glasses. Specifically, it allows a quantitative characterization of the melt equilibrium PSe3/2 + Se -> Se=PSe3/2 describing the stability of four-coordinate P atoms. Using this technique, the effect of isovalent substitution by As, and Te, and of other glass constituents Ge and TI on this equilibrium and on the quantitative phosphorus speciation is studied in detail.

Single crystal ReS2 was characterized using atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The observed atomic-resolution AFM and STM images were interpreted by calculating the total, p(r0), and partial electron density distribution, p(r0, ef), respectively, of a single ReS2 layer. The experimental and theoretical results indicate that the basal plane surface state density is dominated by contributions from the sulfur layer This is in contrast to bulk band structure calculations which would predict that the major contribution to the STM images should be from the Re atoms. Furthermore, the surface-to-tip STM images are found to be quite different from tip-to-surface images. By interpreting STM and AFM data from p(r0) and p(r0, ef) calculations, it is shown that site specific structural and electronic details of the surface can be elucidated.

In this paper we study in situ the intercalation of Li across and along the van der Waals planes of MoS2 single crystals. Li is intercalated according to the band model. The intercalation reaction is inhibited by a Li-S interaction. This interaction is negligible when Li is deposited along the van der Waals planes. The dominance of the intercalation reaction of Li into MoS2 is dependent on the flux of the deposited Li and the substrate temperature.

CuInSe2and related I-HI-VI2 compound semiconductors containing Ga and S are important photovoltaic materials with electrical and optical properties that can be tuned for optimum device performance. Polycrystalline thin films of ternary and multinary compounds from the Cu(In,Ga)(Se,S)2family have already yielded laboratory size solar cells with over 15 % efficiency. Large area photovoltaic modules with over 10% efficiency have also been demonstrated using these materials. In this contribution we present a brief review of the CuInSe2 material characteristics which are important to solar cell performance and their correlation with the processing variables. We concentrate on films obtained by the selenization technique. Selenization of Cu-In precursors is an approach that has yielded good quality CuInSe2films which have been used for the fabrication of high efficiency solar cells.

We have discovered a novel two-phase synthesis of CuInSe2 at 25° from Cu2Se and (C5H5)3In in 4-methylpyridine (4-MePy). An analogous reaction to produce CulnS2 must be run at 140°C in refluxing 4-MePy in the presence of 2-mercaptopyridine. Microscopy of CuInSe2 produced at 25°C shows it to be platelet-shaped crystallites with an approximate particle size of 10 microns, less than 2% C and H, with a small amount of unidentified crystalline impurity. Our results demonstrate that it is possible to produce from solution a material that is ordinarily synthesized in bulk or films at much higher temperatures or using extraneous reagents and/or electrons.

Polycrystalline samples of the chalcopyrites CuInS2, CuInSe2, AgInS2, and AgInSe2 have been prepared from stoichiometric mixtures of the pure elements using microwave irradiation. The reactions were performed in sealed quartz tubes in as few as three minutes. The products were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and X-ray photoelectron spectroscopy (XPS). The surface morphology and shape of the particles produced by this method suggests that the products are formed from liquid melts.

Hafnium nitride films were deposited by ion-beam sputtering, and characterized for their composition, electrical, structural, mechanical and optical characteristics. Films were found to vary widely in their properties, based upon the parameters under which they were deposited. The films were found to have a nitrogen to hafnium ratio of up to 1.45:1, resistivity varying from 10−2 to 105 Ω-cm, as well as widely variable optical characteristics, depending on process variables. Structural characterization of the dielectric phase HfNx (x>l) material by X-ray and electron diffraction reveals a distortion of the hafnium mononitride rock salt structure with increasing amounts of nitrogen, in accordance with previous findings. Infrared spectroscopic characterization of the thin film dielectric phase hafnium nitride optical properties reveals the likely existence of multiple bonding between nitrogen in the material.

Herein we report our efforts to prepare new precursors to niobium nitride (NbN) and tantalum nitride (TAN, Ta3N5) thin films. Treatment of MC15 (M = Nb, Ta) with tertbutylamine in benzene solvent affords complexes of the formula [MCI2 (NtBu)(NHtBu)(NH2tBu)]2. The niobium complex [NbC12(NtBu)(NHtBu)- (NH2tBu)]2 affords NbN films on glass substrates between 500-600 °C, while the tantalum analog [TaC12(NtBu)(NHtBu)(NH2tBu)]2 gives films of Ta3N5 in this temperature range. Treatment of MCI5 (M = Nb, Ta) with 1,1-dimethylhydrazine in dichloromethane solvent affords complexes of the formula [MC12(NNMe2)(NHNMe2)(NH2NMe2)]n. These hydrazido complexes afford cubic MN films upon glass substrates at ≥400°C. Analyses of the films are presented.

Vanadium nitride films reflect infrared radiation and are candidates for solar control coatings for glass. Herein we report our efforts to prepare new precursors to vanadium nitride coatings. Treatment of vanadium tetrachloride with primary alkylamines in dichloromethane affords vanadium chloride amides of the empirical formula [VCI2(NHR)2(NH2R)2]. The characterization and properties of these compounds is presented. The complexes [VC12(NHR)2(NH2R)2] can be sublimed at ca. 100°C (0.1 mmHg) and serve as single-source precursors to vanadium carbonitride films. Films have been deposited in the temperature range of 400-600°C on glass and silicon substrates. The film properties and characterization will be overviewed.

Titanium nitride thin films have been deposited using a novel Hot Filament Chemical Vapor Deposition (HFCVD) technique. In this technique, a resistively heated tungsten wire (∼1700°C) is used to decompose ammonia to obtain highly reactive nitrogen precursor species. This approach allows for low temperature deposition of nitride thin films. In the past, we have used this method to deposit good quality silicon and aluminum nitride films. Titanium nitride thin films have been deposited on Si(100) at substrate temperatures from 500°C to 600°C. These films were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction, Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy. The effects of deposition pressure, substrate temperature and titanium chloride flow rate on film properties have been studied. TiN films with resistivities as low as 80.0 μΩ-cm have been deposited. RBS analysis indicates that the films serve as excellent diffusion barriers for copper and aluminum metallization on silicon.

The reaction of titanium (IV) chloride and amines in an atmospheric pressure chemical vapor deposition (APCVD) has been previously shown to produce high quality titanium nitride films. These films were gold in appearance with high infrared reflectivity and resistivities as low as 80 microhm-cm. In the present study, the carbon content of the amines was systematically increased and the carbon levels in the films measured by XPS. For primary amines carbon contamination was not detected. Films deposited from secondary and tertiary amines had measurable carbon contamination. Correlation of carbon contamination with electrical resistivity and infrared reflectivity is discussed. Scanning electron micrographs and x-ray diffraction of the films are presented.

The organometallic chemical vapor deposition (OMCVD) of transition metal carbides (M = Ti, Zr, Hf, and Cr) from tetraneopentyl-metal precursors has been carried out. Metal carbides can be deposited on Si, A120 3, and stainless steel substrates from M[CH 2C(CH3)3]4 at temperatures in the range of 300 to 750 "C and pressures from 10-2 to 10-4 Torr. Thin films have also been grown using a carrier gas (Ar, H2). The effects of variation of the metal center, deposition conditions, and reactor design on the resulting material have been examined by SEM, XPS, XRD, ERD and AES. Hydrocarbon fragments generated in the deposition chamber have been studied by in-situ mass spectrometry. Complimentary studies examining the UHV surface decomposition of Zr[CH2C(CH3)3]4 have allowed for a better understanding of the mechanism leading to film growth.

Particle bed reactors (PBRs) are being developed for both space power and propulsion applications. These reactors operate with exhaust gas temperatures in the range of 2500 to 3000 K and fuel temperatures which may be hundreds of degrees higher. One fuel design for these reactors consists of uranium carbide encapsulated in either carbon or graphite. This fuel kernel must be protected from the coolant gas, usually H2, both to prevent attack of the kernel and to limit fission product release. Refractory carbide coatings have been proposed for this purpose. The typical coating process used for this is a chemical vapor deposition. Testing of other components have indicated the superiority of refractory carbide coatings applied using a chemical vapor reaction (CVR) process, however technology to apply these coatings to large numbers of fuel particles with diameters on the order of 500 gim were not readily available.

A process to deposit these CVR coatings on surrogate fuel consisting of graphite particles is described. Several types of coatings have been applied to the graphite substrate. These include NbC in various thicknesses and a bilayer coating consisting of NbC and TaC with a intermediate layer of pyrolytic graphite. These coated particles have been characterized prior to test and the results of this characterization will be presented.